Opposed endless conveyors for the continuous molding of rigid foam sheet material are known and have been mounted for movement towards and away from each other for various purposes, for example to vary the thickness of the product, to provide sufficient space and access between the conveyors for maintenance and inspection. Molding pressures for rigid foam sheet material can normally be as high as 3 to 5 pounds per square inch, which pressure produces considerable forces upon the conveyor structure. Therefor, the conveyors must be rigidly mounted, but this rigidity can damage the structure when abnormal pressures are applied, for example locally applied due to a lump or the like.
If screw or other mechanical adjustments were provided for adjusting the conveyors relative to each other, there would be no provision for yielding to the above-mentioned abnormalities, and further the uniform adjustment would be difficult due to accumulated tolerances along the conveyor length, for example, if a chain were used to drive a plurality of screws, the tolerance in the chain would inheritly mean that one end would receive more adjustment than the other end in one direction of adjustment.
The patent to Jetzer U.S. Pat. No. 3,568,245, issued Mar. 9, 1974 employs single acting piston cylinder arrangements for producing a pneumatic clamping pressure urging the conveyor belts together in the molding zone, with minimum spacing being provided by screw adjustment abutments.